The application relates to tire retreading and, more particularly, to a tire retreading system and method that leverages dedicated electric heating pad elements for targeted, individualized control of the curing process for each of one or more tires.
Traditionally, the casings of used tires can be fitted with new tread and placed back into service. Before a tire casing can be retreaded, however, the condition of the casing sidewall must be inspected from shoulder to bead to insure that the casing meets a quality standard suitable for retread. Weak areas within the casing can be marked for repair prior to the eventual application of a pre-molded retread layer. Various conditions which compromise the quality of a tire casing include, among other conditions, zippers, road hazard damage, run-flat abuse and prior repair scars
Once the condition of a casing has been qualified, the casing may be buffed to prepare the old tread surface for receipt of a new retread layer. Proper texture of the casing after being buffed will strengthen the new tread to casing bond. Further, some processes may also buff the undertread contour of the casing, as a desirable undertread contour is known to contribute to a final product that is more likely to meet the performance and wear standards of an OEM tire. Some retread processes employ automated radial buffing systems that may include, among other aspects, casing specification databases and continuous undertread measurement devices that collaborate to ensure optimal undertread depth in the casing after buffing. Alternatively, other retread processes use rudimentary computer controlled or physical templates, circumferential buffing devices and pilot skives to measure undertread thickness.
Once imperfections or defects are detected, whether before or after the buffing process, repairs are made prior to receipt of the new tread. Depending on the particular retread process, repairs may be made via either heat cure methods or chemical cure methods. Generally, heat cure methods are preferred in the industry, as the result is an improvement over chemical cure methods with regards to final adhesion and tear resistance.
After inspection and repair, a buffed tire casing is ready to receive a new tread. First, a hot layer of cushion gum is extruded or wrapped onto the casing to promote a strong tread-to-casing bond. Notably, the layer of cushion gum not only provides a bonding layer between the casing and the new tread layer, but also serves to fill skives and “buzzouts” that may be present on the surface of the casing. After the cushion gum layer is applied, a pre-molded tread layer is wrapped over the cushion gum and temporarily secured in place.
Next, the casing, cushion gum and tread layer retread package is placed inside a vacuum envelope. Some processes utilize a single vacuum envelope applied over the outside of the retread package and sealed against the beads of the casing with rings. Other processes, however, apply inner and outer vacuum envelopes that work together to seal around the entire retread package and apply uniform pressure to the exterior and interior surfaces of the retread package during molding. Other processes use a combination of a vacuum envelope on the outer application to apply a pressure to the retread package during the molding process. A vacuum is applied to the envelope(s), thus pressing the casing, cushion gum layer and tread layer together with a uniform pressure. The enveloped tire package is then placed inside a heated curing chamber for the period of time required to bond the layers together and achieve proper cross-linking or curing of the tire.
Multiple retread packages, each comprised of a casing, cushion gum layer and retread layer that are surrounded by a vacuum envelope, may be placed inside a curing chamber or autoclave. Once inside, electric or steam heating elements are used to heat the air inside the curing chamber to a temperature suitable for curing the retread packages. The heated air is circulated around the multiple retread packages in order to cure the tires.
One of ordinary skill in the art will recognize that there are many disadvantages to the retread methods and systems presently known in the art. A few of the disadvantages are:                i. By using a single, large heating element to heat the air inside the autoclave, present systems and methods are susceptible to manufacturing downtime when a heating element fails.        ii. Because the heated air must be constantly circulated to effectively cure the tire packages, present systems and methods are prone to mechanical failure of the fans.        iii. To heat the air within the autoclave of present systems and methods, it is also necessary to heat the entire curing chamber. Heating the entire chamber is an inefficient, and costly, use of energy.        iv. Because present systems and methods are limited to a single air temperature and curing time, a plurality of retread packages curing in the chamber must comprise identical or similar components. That is, the tires that are being retread in a given curing cycle must be of the same type. This limitation forces manufacturing methods using present retread systems to apply an inefficient “batch” approach.        v. Because thermal energy intended for curing the retread packages is wasted in the present systems and methods by heating the air and curing chamber, curing cycle times are unnecessarily long.        
Therefore, what is needed in the art is a system and method for retreading tires that overcomes one or more of the above limitations and problems, as well as other limitations and problems, of the prior art.